Energy costs: How cotton gins can save money

Continually rising energy costs for cotton gins make it all the more important to achieve optimum levels of operating efficiency, says Tommy Valco, USDA/ARS technology transfer coordinator at Stoneville, Miss.

Two operating practices can help ginners increase efficiency and save money on energy costs, based on research at the USDA/Agricultural Research Service’s Cotton Ginning Laboratory at Stoneville, Miss.

TOMMY VALCO

“Energy use has been an important concern at all our research labs, and all ginners are aware of continually rising energy costs,” says Tommy Valco, USDA/ARS technology transfer coordinator at Stoneville, Miss., who discussed the studies at the summer meeting of the Southern Cotton Ginners Association at Biloxi, Miss.

An energy monitoring project, involving on-site investigative studies at commercial gins, was designed to determine what kind of energy is being used, how, when, and where, for the different gin components, he says.

“We went into the gins and hooked up ammeters and data loggers to measure energy used, as well as power factors, for each operation. This helped to identify what was going on, how the efficiently system was working.

“Our findings very clearly show that the number of kilowatt hours per bale is reduced significantly as the number of bales per hour increase. One gin we studied averaged a very low 26 kWh per bale, which was amazing — most gins never hit that kind of number. But we do have some gins operating at 30 kWh, which is a very good number. On average, most gins are in the 40 to 45 kWh range.”

A key finding from the studies, Valco says: “You need to keep the gin as fully loaded as possible. Too many times, we find gins running at only 70 percent to 80 percent of capacity, which is just burning energy needlessly. If we can keep them running at 85 percent to 90 percent of capacity, they’re operating much more efficiently.”

A survey of Mid-South gins was conducted a few years ago to evaluate feeding rates for the seed cotton cleaning system, he says.

“Even though ginning equipment manufacturers all have good equipment, there wasn’t a lot of data available about loading rates. We wanted to be able to provide information that will be helpful to ginners, as well as to manufacturers in improving equipment design in order to operate as efficiently as possible.

“The Cotton Ginners Handbook shows a maximum feeding rate of about 2.5 bales of hour per foot of width,” Valco says, “but many gins are running much higher than that. Our survey showed some exceeded 4 or 4.5 bales per hour per foot.

“This stimulated a new research project. After upgrading our micro-gin at the Ginning Laboratory to increase capacity, we were able to increase the feeding rate to 3 to 4 bales per hour per foot of width, and in some situations as much as 6 bales per hour. This allowed us to update our data on cylinder cleaning settings, spacing, speed, etc.”

The study identified such factors as how much fiber is lost as seed cotton cleaning rate increases, the quality of the ginned cotton — “which is critical to the process” — and the variability of cleaning from one year to another.

“We need to keep gin stands fully loaded, insure that cotton enters the gin at the desirable moisture content, and minimize air usage as much as possible,” Valco says.

How gin shutdowns are handled can also affect operational efficiency and energy use, he notes.

“The data we’ve collected show if the idling time will be 12 minutes or greater, it’s better to shut down the gin, then start it back up after the problem is solved.”

Analyzing particulate matter emissions

All three of the USDA/ARS ginning labs have been working on a project to characterize particulate matter emissions from cotton gins, Valco says.

“This is a five-year project, including 7 different gins, one in the Southeast, one in the Mid-South, two in Texas, one in New Mexico, and two in California. It’s a wide-ranging program, with support from Cotton Incorporated, the National Cotton Council, and the National Cotton Ginners Association, to gather as much data as we possibly can to help alleviate some of the regulatory requirements gins are facing with emissions. We want to keep a buffer between the regulatory agencies and our gins.

“Most of the problems were in the California region, where regulations are particularly strict. The study has helped to address a lot of the issues they were having.

“We collected PM10, PM2.5, and total particulate matter data — several million samples at each gin. It’s a tremendous data set that will, hopefully, allow state regulators to develop regulations that make sense.

“We’re now in the process of writing papers from these data and getting results into technical journals. The work has already created some good results in the California area — we found they were significantly over-predicting PM2.5 levels. The data have also been useful to gins in Texas.

“We’re putting final touches on the paperwork. It’s a study we can really be proud of, with facts that will be useful in dealing with particulate matter regulations.”

Another research project has been evaluating commercial bale moisture measurement devices, Valco says.

“As an industry, we finally worked out the issues related to adding moisture to bales, and ginners are now doing a very good job of maintaining moisture, without overdoing it. We know we need to add moisture back to bales to make the gin system operate properly.”

This study looked at the effectiveness of measurements with commercially available moisture meters. “They included the TexMax meter from Samuel Jackson, which a lot of gins use; the Intelligin, a resistance-type moisture sensor in the lint flue, which does an extremely good job; and the Delmhorst bale probe. These were compared to standard oven moisture testing.”

The study looked at 731 bales over several different time periods.

“The Intelligin provided the best and most accurate data,” Valco says. “The problem is that the data are collected prior to the moisture restoration system. Moisture content in the lint flue ranged from 4 percent to 5 percent; 90 percent of the bales had moisture content ranges between 4 percent and 6 percent, with a mean moisture of 5 percent.

“We’d like to have it higher than that. We know that at 4 percent to 5 percent moisture, the brittleness of the cotton fiber and potential for fiber breakage increase. We like to see fiber moisture content between 5 percent and 6 percent to maintain fiber integrity, while providing an excellent cleaning opportunity.

“Managing moisture is always a difficult process. With the Intelligin system, we had no bales that got even close to the 7.5 percent maximum bale moisture content. With moisture restoration, we were able to introduce up to 2 percent moisture back into the bale, which is good. This was a high capacity system and did a good job.”

The handheld Delmhorst meter was one of the most accurate measurement devices, Valco says, “but it needs to be corrected for temperature. For every 20 degrees above 70 degrees F., the owner’s manual notes that you should reduce the moisture reading by 1 percent.

“Most bales come out of the press at 110 to 120 degrees F., depending on ambient conditions, so a 2 percent reduction from the meter reading is relatively safe.

“We were getting good data from this meter, but many ginners don’t like to use a handheld meter because they’re labor-intensive.”

The TexMax meter read 1.8 percent too high, Valco says. “You can get good moisture measurement readings with this technology, but you do have to calibrate it for your gin. After calibration, most readings averaged about 5.2 percent moisture, which is similar to corrected readings for the handheld meter.

“The Delmhorst probe produced some of the best, most economical data, when you do the needed temperature correction. Intelligin is by far one of the most accurate moisture measuring systems, but it takes the measurement prior to moisture restoration, and not many gins use this system. The TexMax, a microwave moisture measuring device, also does a good job as long as it’s calibrated.”

The study documents that “we have some good technology for measuring bale moisture,” he says, “but for accurate results, the systems have to be accurately calibrated and maintained.”

Measurements of moisture content levels can be done for ginners at the USDA/ARS Stoneville laboratory, Valco notes. “Take plenty of samples, double bag them in quart-size freezer bags, label and send them Rick Byler (research leader at the lab) and he’ll send the data back to you, no charge.”